Studies of a variety of immunologic and physiologic parameters of isolated islet allografts and isografts are all described. To evaluate possible mechanisms of islet allograft rejection, immunofluorescence and chromium release studies will be used to determine the potential role of antibody in islet destruction. Various regimens known to alter either host immunoreactivity to or donor immunogenicity of whole organs will be applied to islet allografts in an attempt to prolong their survival. Physiologic studies of islets implanted to various host sites will be performed, measuring their effects on glucose metabolism, in addition to the insulin and glucagon responses to a variety of known stimulants of these hormones. Several in-vitro and ex-vivo techniques will be used to determine what effects successful islet transplants have upon the abnormal glucagon dynamics of experimental diabetes.